1. Field of the Invention
The present invention relates generally to vehicle headlights, and more particularly, to a vehicle headlight, in which a simple light emitting unit is employed for selective lighting of a high-beam at night or a low-beam during crossing with an oncoming vehicle.
2. Background of the Related Art
In general, the headlights, mounted on the front of a vehicle to ensure an adequate field of view of a driver when driving the-vehicle at night, are required to have a luminance specified by law, and not to obstruct the vision of oncoming drivers.
That is, the headlight is required to form a running beam (so called an upper direction beam, or a high beam) for securing a long range of view during regular running, and a crossing beam (so called a low direction beam, or a low beam) when crossing with an oncoming vehicle so as to prevent the light beams from obstructing the vision of oncoming drivers while securing a certain extent of range of view.
A halogen lamp is widely used in a conventional headlight. The halogen lamp is provided with two filaments, that is, a filament for irradiating a high-beam and a filament for irradiating a low-beam, so a high-beam mode or a low-beam mode may be selectively operated as desired. In this case, the filament for irradiating a low-beam is installed inside the vessel-shaped lamp.
However, when the halogen lamp, which is provided with two filaments, is compared with a gas-discharge lamp which is widely used now, the halogen lamp is inferior in performance to the gas-discharge lamp. Thus, there is a growing tendency to use the gas-discharge lamp for a headlight, because the gas-discharge lamp radiates white light, which is about three times as bright as the conventional halogen lamp, thus making it easy to distinguish objects, and uses two-thirds of the halogen lamp's electric consumption, and is semi-permanent. However, since only one gas-discharge lamp is installed in such a headlight, there is restriction, imposed on the design of the headlight.
That is, it is impossible to develop a gas-discharge lamp having two filaments, that is, two light emitting units so as to irradiate both a high beam and a low beam, so the above-mentioned problem occurs.
In order to overcome such a problem, there has been proposed a method where a light emitting unit is operated by a small-sized motor to instantaneously move upward or downward. However, such a method has a problem that it has a complicated mechanical mechanism because the rotating movement of the motor must be converted into a rectilinear movement, the manufacturing cost is increased, and the operation is slow. For these reasons, the gas-discharge lamp is not widely used in the headlight.